Add configure_mirror.sh back to tripleo-centos-7
Add configure_mirror.sh back to tripleo-centos-7

This is needed to test jobs in the experimental-tripleo pipeline. For
the moment, we added a CNAME record to rax-dfw to validate jobs with
correctly with our pip / wheel / centos mirrors.

Change-Id: I34b8d9ff121ed68184be373f6f0d21e55e3f631c
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

openstack-infra/project-config,Tesora/tesora-project-config,dongwenjuan/project-config,Tesora/tesora-project-config,openstack-infra/project-config,dongwenjuan/project-config